The long-term goal of this research program is to develop and alternative contraceptive technology based on the immune response to sperm-specific Lactate Dehydrogenase C4 (LDH-C4; LDH-X). Immunological control of fertility has been demonstrated in a variety of systems, and immunization with LDH-C4 does have a contraceptive effect. To exploit this phenomenon in a practical system, the natural product must be replaced with small synthetic peptides that elicit an immune response to the native protein. The design of these peptides will be based on an immunological map of LDH-C4. Monoclonal antibodies to LDSH-C4 will be used to map the antigenic structure of this protein. The domains recognized by these antibodies will be identified with peptides derived by chemical and enzymic cleavage of LDH-C4, by classical peptide synthesis, and by surface simulation synthesis. Peptides containing these antigenenic domains will be used to optimize the immunization protocol. Both systemic and local immune responses to the synthetic antigen will be exploited for immunosuppression of fertility based on LDH-C4.